A seat belt assembly is mounted in a vehicle for restraining an occupant in a seat of the vehicle during a sudden deceleration of the vehicle, e.g., during a vehicle impact. The seat belt assembly includes a retractor having a rotatable spool with a webbing wrapped about the spool. The webbing is extendable from the spool, i.e., by rotating the spool, to allow the webbing to be extended across the occupant and engaged with a buckle via a clip on the webbing. The spool is spring-loaded to bias the webbing toward the retractor to pull the webbing against the occupant when the clip is engaged with the buckle and to retract the webbing onto the spool when the clip is disengaged with the buckle.
The retractor may include a pretensioner that is activated to rotate the spool to retract the webbing during a sudden deceleration of the vehicle, such as when a vehicle impact is sensed, to reduce or eliminate slack in the webbing and pull the webbing toward the occupant. The vehicle may include an impact sensing system that senses impact of the vehicle, and the impact sensing system may be in communication with the pretensioner to instruct the pretensioner to activate when impact of the vehicle is sensed. As the pretensioner causes the spool to retract the webbing, the webbing pulls the occupant against the seat. This positions the occupant for interaction with inflating front airbags and reduces the likelihood that the occupant slides forward under the webbing, i.e., reduces the likelihood of “submarining.”
However, during normal operating conditions of the vehicle, retraction of the webbing onto the spool may create slack in the webbing on the spool. During an impact of the vehicle, forward momentum of the occupant pulls this slack of the webbing from the spool. The slack of the webbing on the spool counteracts the pretensioner. As such, there remains an opportunity to design a retractor that reduces the counteraction of the pretension by slack in the webbing on the spool.